I guess its kinda like PIN number (
Personal
Identification
Number......number)
but nothing like SHT (
Stop.
Hammer
Time)
GTM time is actually GMT

GMT time stands for
Greenwich
Mean
Time.....time
as Austin Powers would say "too many 'times', baby!" (if that's at all possible


)
....oh right, answering a question...
another method used is UTC which stands for
Coordinated
Universal
Time, or Universal Time, Coordinated.
have a look at this info about UTC on
world clock at
www.timeanddate.com/